name:_______________________
student ID:_____________________
Genetics L311 exam 3
November 21, 2014
Directions: Please read each question carefully. Answer questions as concisely as possible.
Excessively long answers, particularly if they include any inaccuracies, may result in deduction
of points. You may use the back of the pages as work sheets, but please write your answer in the
space allotted. However, you must show all your work. Clearly define your genetic symbols.
We will not make guesses as to what a particular symbol is intended to mean. Also, don’t assume
that strains are true-breeding unless this is stated in the question. Finally, show all your work.
Good luck.
page 2
_______
(20 points possible)
page 3
_______
(30 points possible)
page 4
_______
(20 points possible)
page 5
_______
(18 points possible)
page 6
_______
(12 points possible)
total
_______ (of 100 points possible)
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name:_______________________
student ID:_____________________
1. Short answers (2 points each, 20 points total)
A. An organisms with four sets of chromosomes, all derived from the same species, is
said to be autotetraploid .
B. A cell or individual with some deviation from a whole multiple of the haploid or
monoploid chromosome complement (eg. having one extra chromosome or missing one
chromosome) is said to be aneuploid .
C. Usually sterile, monoploids are the rare products of defective chromosome
segregation in which the individual has only one copy of each of the chromosomes.
D. The mitochondria , major sites of ATP synthesis, are small cytoplasmic organelles
that include their own genomes.
E. The ability of some phage to transfer only a specific portion of a bacterial
chromosome between bacteria is called specialized transduction .
F. The general approach of moving from a cloned gene to identifying a mutation in that
gene is called reverse genetics .
G. Expression of as few as four genes in differentiated cells can cause them to dedifferentiate, producing induced pluripotent stem cells.
Please provide concise definitions of the following terms:
H. nucleoid: Region of bacterium where the DNA is located.
I. prophage: Bacteriaphage genome integrated into a host cell’s genome.
J. restriction endonuclease: Enzyme that binds specific sequence of DNA and cuts it.
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name:_______________________
student ID:_____________________
2. You have decided that you really want to get into the movie business and furthermore that
your first movie will be about sharing your life with 3 genetic clones of yourself. To make it
authentic you decide that you should first generate those three clones of yourself.
A. Please describe briefly how you will go about cloning yourself (8 points).
1. Obtain human eggs
2. Remove nucleus
3. Fuse enucleated eggs with your somatic cells
4. Allow to develop
B. At present cloning is fraught with difficulty. Please give two ways in which your attempt to
clone yourself might go awry (I’m not looking for reasons why your clone might be different
from yourself but rather potential problems with the process itself (4 points).
Many of the embryos won’t “take” (i.e. it’s extremely inefficient)
Many of those that do develop have problems that can lead to death, often around the time
of birth.
3. After being marooned on an uninhabited island, you discover an interesting species of beetle.
You observe two different strains: one with blue wings and another with red wings. You decide
to cross true-breeding blue-winged females with true-breeding red-winged males. The resulting
progeny are all blue-winged. You then cross the F1’s, which results in all blue-winged F2’s.
A. What modes of inheritance are consistent with these results (6 points)?
maternal effect of extranuclear
B. After lighting a signal flare, you decide you still have time to cross the F2’s together before
being rescued. You find that the resulting progeny are a mix of blue-winged and red-winged.
Which of the modes of inheritance that you listed above best explains this new result (6 points)?
maternal effect
C. What is the phenotypic ratio observed in the F3 generation (4 points)?
3:1 blue:red
D. After being picked up by the Coast Guard, you head straight to the lab
and clone the gene responsible for the beetle’s wing color. You then
sequence the DNA. The following autoradiogram shows the sequence of
a small region of the gene. What is the sequence of this region? Be sure
to indicate the 5’ and 3’ ends (2 points).
5’-GAACTATCTCGCATC-3’
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name:_______________________
student ID:_____________________
4. Imagine that you are counseling a couple who have just had a child born with Down
syndrome, which typically results from trisomy 21. The couple’s first child was also affected by
Down syndrome. When you examined the child’s karyotype you find 46 chromosomes.
A. How might you explain this result (4 points)?
Could be a Roberstonian translocation involving chromosome 21
B. The couple wish to have another child. Which of the following provides the best estimate of
the probability that the couple’s next pregnancy will be affected by Down syndrome (2 points)?
i. the couple’s next pregnancy is certain to be affected by Down syndrome (probability = 1)
ii. the couple’s next pregnancy is certain not to be affected by Down syndrome (probability = 0)
iii. the probability is the same as for the general population, which is ~1/25,000
iv. the probability is higher than the general population risk, and may be as high as 1/3
v. based on Mendelian principles, the probability is exactly 1/2
5. You have identified mutations in a gene, asm, that produces short hair in the rare Himalayan
Yeti. To understand its function, you decide to clone the gene. Interestingly, your good friend
Seymour Myths, a scientist at the Research Institute of the Himalayas has shown that the asm
gene is tightly linked to the ylw gene.
A. Please name the method you would use to clone asm (you do not need to provide the steps
involved, 3 points).
chromosome walk or positional cloning
B. You are so intrigued by Yeti genetics that you purify a protein called Fng that seems to
regulate tooth development. You use the purified protein to immunize rabbits, produce a high
affinity antibody that specifically recognizes Fng. Please briefly outline how you would clone the
fng gene (i.e. the gene that encodes FNG). You do not need to give all the steps, just enough
information to know the method you will use to find the clone (3 points).
make a cDNA library using the antibody as a probe
C. Your research indicates that a mouse homolog to the yeti asm gene functions similarly. To
further study asm function, you decide to mutate the mouse asm homolog. Assume that you have
cloned the mouse asm gene, please describe how you would generate homozygous mouse asm
mutants. Include a picture of the vector that you would use (8 points).
asm 5’
neoR
asm 3’
TK
1. Infect ES cells from black mouse using vector shown above. 2. Select for recombinants in
neomycin and ganciclovir. 3. Verify that recombinants had deletion within asm by
Southern or PCR. 4. Mix engineered ES cells with embryo derived from white mouse. 5.
Implant into pseudopregnant mouse to produce chimeric mice. 6. Cross chimeric X white
to find those chimeric mice that produce all black offspring. Use Southern or PCR to ID
hets. 7. Cross hets to generate homozygotes.
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name:_______________________
student ID:_____________________
6. You are studying the genetics of the rare and ugly hairless llama when you notice that in some
individuals the 10th chromosome is quite unusual. The normal chromosome is shown on the top
and the unusual one is shown below.
A. Give the specific name of the chromosomal
alteration that caused the strange chromosome
(2 points).
pericentric inversion
B. Show the 2 chromosomes synapsed in meiosis (in a heterozygous individual). Include the
genes (6 points).
This is hard to draw on the computer. Check your class notes.
C. Please show the products of meiosis in which a single crossing-over event has occurred
between W and the centromere (4 points).
TUVW•XYZ
TUX•WVYZ
TUVW•XUT
ZYX•WVYZ
7. Strains heterozygous for each of five Drosophila mutations, a – e, and for each of five
different deletions, 1 – 5 are generated. The table below shows whether such strains displayed
wild type (+) or mutant (-) phenotypes. The figure illustrates the region deleted in each deletion
strain (region deleted indicated by a bar) as determined by cytological examination of polytene
chromosomes.
del 1
del 2
del 3
del 4
del 5
deletion 1
deletion 2
deletion 3
deletion 4
deletion 5
a
+
–
–
–
+
b
–
–
+
–
+
c
+
–
–
–
–
Assign each recessive mutation to the relevant region of the chromosome (6 points).
b
a
c
d
e
5
d
+
+
+
+
–
e
+
–
+
–
–
name:_______________________
student ID:_____________________
8. In two different interrupted mating experiments, you obtain the data shown below for the time
of entry. All experiments were conducted using Hfr strains (Hfr1 and Hfr2) derived from the
same original strain of E. coli.
jes
kat
pol
kev
sha
mel
Hfr1
6 min
13 min
14 min
19 min
35 min
50 min
Hfr2
kev
pol
kat
jes
mel
sha
8 min
13 min
14 min
21 min
65 min
80 min
A. Draw a genetic map showing the location of and distances between each gene on the bacterial
chromosome. Please include the Hfrs (8 points).
hfr1
6
jes
7
kat 1 pol
5
kev
8
hfr2
8
sha
15
mel
38
B. Two of the genes map very near one another (within a minute). Time of entry mapping does
not provide a very accurate position for genes that are close to one another. Briefly describe how
you could more accurately determine the relative positions of these two genes, including the
steps involved. Assume the genes are required to synthesize a compound of the same name (eg.
the kat gene would be required to synthesize Kat, pol makes Pol, etc., 4 points).
Pol and kat are within one minute of one another. To map them more accurately we would
use a generalized transducing phage, allowing it to infect wild type cells. After we would
purify phage and allow them to infect pol- kat- cells. We would plate on plates lacking Pol
and replica plate to plates lacking Kat. This would confirm that these two genes are close
together. We might include other genes that we know reside in the area to further develop
the genetic map in this region.
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